Diurnal variability in soil nitrous oxide emissions is a widespread phenomenon

Manual measurements of nitrous oxide (N2O) emissions with static chambers are commonly practised. However, they generally do not consider the diurnal variability of N2O flux, and little is known about the patterns and drivers of such variability. We systematically reviewed and analysed 286 diurnal data sets of N2O fluxes from published literature to (i) assess the prevalence and timing (day or night peaking) of diurnal N2O flux patterns in agricultural and forest soils, (ii) examine the relationship between N2O flux and soil temperature with different diurnal patterns, (iii) identify whether non-diurnal factors (i.e. land management and soil properties) influence the occurrence of diurnal patterns and (iv) evaluate the accuracy of estimating cumulative N2O emissions with single-daily flux measurements. Our synthesis demonstrates that diurnal N2O flux variability is a widespread phenomenon in agricultural and forest soils. Of the 286 data sets analysed, similar to 80% exhibited diurnal N2O patterns, with similar to 60% peaking during the day and similar to 20% at night. Contrary to many published observations, our analysis only found strong positive correlations (R > 0.7) between N2O flux and soil temperature in one-third of the data sets. Soil drainage property, soil water-filled pore space (WFPS) level and land use were also found to potentially influence the occurrence of certain diurnal patterns. Our work demonstrated that single-daily flux measurements at mid-morning yielded daily emission estimates with the smallest average bias compared to measurements made at other times of day, however, it could still lead to significant over- or underestimation due to inconsistent diurnal N2O patterns. This inconsistency also reflects the inaccuracy of using soil temperature to predict the time of daily average N2O flux. Future research should investigate the relationship between N2O flux and other diurnal parameters, such as photosynthetically active radiation (PAR) and root exudation, along with the consideration of the effects of soil moisture, drainage and land use on the diurnal patterns of N2O flux. The information could be incorporated in N2O emission prediction models to improve accuracy.

Automated summary

The study found that diurnal N2O flux variability is a common phenomenon in agricultural and forest soils, with around 80% of data sets exhibiting diurnal patterns, peaking during the day in 60% of cases. Contrary to expectations, strong positive correlations between soil temperature and N2O flux were found in only a third of the data sets, with other factors such as land management and soil properties potentially influencing the occurrence of diurnal patterns.